Almost all philosophers, ancient and modern, fearing an eternal confusion of the elements, were they all endowed with weight, conceived the two uppermost to be furnished with a certain levity, by means of which they bounded up on high, each to occupy its peculiar place, like as the two lower ones are pushed downwards by their own weight. But having clearly shewn in the last Essay, that levity is not necessary for that effect, weight alone being sufficient, I embrace the maxim, which they themselves have prudently laid down, that we should never multiply existences unnecessarily; assuming that God and Nature do nothing in vain, (which they also teach.) I think it would be otherwise were we to admit levity, since it is of no use.

John Rey (1583–1645) (or, in French) Jean Rey, was a physician of Périgord, France who in 1630 published a tract on calcination, or oxidation of metals, after being notified by Brun, an apothecary of Bergerac, France, of Brun's experiments (as early as 1629) on the calcination of tin. Brun had melted 2 pounds six ounces of tin, and after 6 hours the resulting calx weighed seven ounces more than the original tin. More than one hundred and forty years before Antoine Lavoisier, John Rey recognized that in the calcination of lead or tin, part of the air provided an increase in mass to the calcined metal oxide. His work was eclipsed first by the phlogiston theory and then later, by Lavoisier's discoveries disproving the existence of phlogiston. Lavoisier's oxygen theory confirmed Rey's earlier report, of which Lavoisier claimed he was unaware. After the presentation of Lavoisier's 1775 memoir at the Académie des sciences, Pierre Bayen (1725-1798) wrote a letter to Abbé François Rozier, director of the journal Observations sur la Physique, sur l'Histoire naturelle and sur les Arts, to ask him to publish an update notice, recognizing the priority Rey's work.